On the other hand, most jobs in the military aren’t combat positions. Doctors and nurses and IT experts and intel analysts and the like don’t need to be as strong and have as good cardio as combat troops. They bring different skill sets to the table.
Yes, and no. Yes and no.
Just as each MOS is different, so is each branch.
When somebody talks about the Marine Corps, then you really are talking about a branch that is unique. The "Every marine is a Rifleman" is really taken to heart there.
I spent a decade in the Grunts as a Marine. And when our Battalion went "out to the field",
everybody went. And we all marched. Infantrymen, cooks, Corpsmen, admin clerks, supply guys, Motor-T, heck even the Battalion Chaplain was right there with his pack, marching alongside the rest of us. Nobody was left behind, everybody marched out with full packs. And once we got to our destination, everybody dug in and set up their fighting positions before they went back to their "regular jobs".
This is something I never saw in the Army. We got in our trucks, drove to our destination, then the Force Protection section set up the defenses and pulled security so that the clerks and mechanics could do their jobs. And it was always funny when we had a simulated attack, and the mechanics never had a clue where their fighting positions were or how to react other than "point at the bad guys and shoot".
Each branch in the military is different, and has very different doctrine and traditions. And when the messy brown stuff hits the oscillating air foils, this is often what makes the difference. It is why to the Marines, events like Chosin and Khe Sahn are still important lessons. They performed as they did because of their belief that "Every Marine is a rifleman". And they expect the same standards (even if not the same training) from every member.